Zhenchen Liu

This study examines the hovering and forward-flight stability of a heavy-lift coaxial unmanned helicopter with a suspended payload. A six-degree-of-freedom dynamics model is developed, coupling the rotor, fuselage, and a rigid-body sling via a universal joint, while neglecting rotor–payload aerodynamic interference for sling lengths exceeding eight rotor diameters. Trim calculations for hover and steady forward flight are compared with F-500 flight data, showing better agreement for the longitudinal trim quantities than for the lateral quantities. Stability analysis using static derivatives and eigenvalue decomposition reveals that the suspension system degrades airspeed stability but has little effect on angle-of-attack stability. At the reference flight condition, the Dutch-roll eigenvalues have a positive real part, indicating an unstable lateral-directional oscillation. Parametric studies indicate that increasing forward speed worsens the longitudinal phugoid mode, whereas heavier payloads enhance damping in both longitudinal and lateral-directional modes. Enlarging the payload’s cross-sectional area improves non-oscillatory mode stability but barely affects lateral dynamics. These findings provide theoretical guidance for design and safe operation, highlighting the importance of speed regulation and payload configuration optimization to enhance flight safety.

Ammonia, a toxic and volatile pollutant commonly found in chemical industrial environments, requires reliable real-time detection to ensure industrial safety and effective environmental monitoring. Conventional gas sensors typically operate at elevated temperatures, resulting in high power consumption. Moreover, pure metal oxides and conductive polymers often suffer from significant aggregation and exhibit suboptimal sensing performance under ambient conditions, limiting their practical applications. In this study, hierarchical porous V₂O₅/PANI composites were synthesized via a straightforward one-step coprecipitation method combined with in situ polymerization. The interlaced architecture of polyaniline (PANI) and vanadium pentoxide (V₂O₅) effectively reduces structural aggregation and increases the availability of surface active sites. Furthermore, the synergistic interaction at the bi-phase interface significantly enhances charge carrier transport, leading to improved ammonia-sensing capabilities at room temperature. Notably, the composite containing 20% V₂O₅ demonstrated superior response, selectivity, and reproducibility toward 10 ppm NH₃. Due to its simple fabrication process and room-temperature operation without external heating, the developed V₂O₅/PANI composite sensor holds significant potential for practical applications in low-concentration ammonia detection under ambient conditions.